Wind energy systems as are used nowadays increasingly as alternative energy suppliers on account of dwindling energy resources are normally constructed on land or off the coast at sea. Such a wind energy system can include a plurality of wind energy installations, which can be connected to one another in different ways. Tidal power energy systems have in turn been installed on the seabed, wherein the tidal range or the flow of the seawater is utilized as primary energy source. Such a tidal power energy system can include a plurality of tidal energy installations, which likewise can be connected to one another in different ways.
An energy installation can include a wind turbine or water turbine, which is connected to a generator, wherein a converter unit is provided, which is connected on the generator side to the generator and can be connected on the grid side to an electric power grid. The converter unit can be connected to an electric power grid directly or via a transformer, which is used for voltage adjustment. The electric power grid may be an AC voltage grid or a DC voltage grid, wherein in the case of a DC voltage grid the above-mentioned transformer naturally is not required.
During normal operation of the energy installation, the generator is driven by the wind turbine or water turbine, wherein the electrical energy generated by the generator is fed via the converter unit into the electric power grid. The energy installation can include an auxiliary energy unit, which for example is used to supply power to the converter control, the turbine control, and/or the navigation lighting system in the case of a wind turbine and to supply power to the oil pumps for lubrication of the bearings of the moving parts of the energy installation (i.e., generally to cover the intrinsic energy demand of the energy installation).
During normal operation of the energy installation, the auxiliary energy units draws the electrical energy necessary for the above-mentioned power supply from the electric power grid and is for this purpose connected directly or via a transformer to the electric power grid. In the case of a DC voltage grid, this transformer naturally is not required. In addition, the energy installation can include an energy storage unit, which for example can be formed as a battery or as a fuel-operated emergency power unit, wherein the auxiliary energy unit is connected to the energy storage unit. In the event of a separation of the energy installation from the electric power grid, whether as a result of a grid-side fault or for maintenance or commissioning purposes, the auxiliary energy unit can no longer remove electrical energy from the electric power grid and instead removes the electrical energy necessary for the above-mentioned power supply of the energy installation from the energy storage unit.
In the case of an energy storage unit formed as a battery, the electrical energy to be removed therefrom can be drawn for example only for approximately one day. This short period of time is not acceptable for example in the event of maintenance or commissioning works on the energy installation. If the energy storage unit is formed as a fuel-operated emergency power unit, the fuel supply must always be ensured, which is complex, inefficient and costly.